The intimate life of cockroaches
Résumé
Mate choice theories predict that animals evolved strategies to bias their mating towards partners
providing the best reproductive returns. Females are generally thought to be more selective
than males because of their investment in offspring. However recent evidence suggests that male
mate choice has been underestimated in a number of species and mutual mate choice may be more
common that initially thought. To reveal and to disentangle roles played by each sex in a mating
system, we assume that detailed analyses of precopulatory behavioural sequences are necessary.
Here, we report for the first time male and female selectivity in the cockroach Blattella germanica
(L.). In this group-living species where adults do not disperse, kin recognition is a key
factor for choosing genetically dissimilar mates. Binary choice tests showed that females given a
simultaneous choice between two identically related males, either two siblings (r = 0.5) or two
non-siblings (0 ≤ r < 0.5), mated preferentially with the male that displayed the most vigorous
courtship. When given a choice between a sibling and a non-sibling male, females still mated with
the one that displayed the most intensive courtship, which was most often the non-sibling male.
When males were given a simultaneous choice between two females, they invested more vigorously
in courtship towards non-sibling than toward sibling females, independently to any active role of
females.
Our results revealed an adaptive mating system with mutual mate choice, where sexes select
their mates on different criteria and at different phases in the precopulatory sequence. Males
attracted by females come into antennal contact with them, assess their relatedness and invest
preferentially in courting non-siblings, whereas females mate with the male that courts the most
vigorously. Resulting pairings allow close inbreeding avoidance within aggregates and thereby an
important decrease of reproductive success (12%).